1. Field of the Invention
This invention relates to priming compositions for use in cleaning substrates and promoting adhesion between photoresists and various metallic and non-metallic substrates. This invention further relates to articles manufactured with the priming compositions, and to methods of treating substrates and bonding photoresists to the treated substrates.
2. Description of the Related Art
The coating of substrates with positive-type photoresist (photochemical degradation) or negative-type photoresist (photochemical crosslinking) for the purpose of recording positive or negative information through photolithography is known. This technique is practiced in the manufacture of, for example, semiconductors, optical media (e.g., compact discs), holography, and other related microelectronic components. It is also known in this industry to use primers to treat the substrates in an effort to improve adhesion between a subsequently applied layer of photoresist and the substrate. Improvement in adhesion is performed with the intention of providing advantageous properties, such as prevention of delamination and undercutting, as well as the significant reduction, if not elimination, of adhesion failure caused by the generation of nitrogen gas during exposure of the photoresist (a phenomena generally known as popping). In the field of optical media, such as CD""s and DVD""s, primers desirably reduce jitter and improved block error rate.
Current photoresist adhesion promoters include silanes, of which hexamethyldisilane (xe2x80x9cHMDSxe2x80x9d) is most common. Other common priming agents include, but are not limited to, titanates, SnCl2, and various silane (SinH2n+2) compounds. HMDS is believed to form a bridge bond, or crosslinking, between the photoresist and the substrate, thereby improving adhesion. However, HMDS has several drawbacks that deprecate this advantage. For example, HMDS is insufficiently tolerant to water so that the presence of moisture between the substrate and HMDS may result in adhesion failure. As a consequence, additional processing steps, such as baking, often require complete drying of the substrates prior to the application of HMDS. Additionally, the formation of covalent bonds or crosslinking between the HMDS and both the substrate and photoresist significantly increases reconditioning requirements of substrate recycling. Mechanical etching is usually required to completely remove these conventional primers. Furthermore, silanes require the presence of reactive hydroxyl groups on the surface of the substrate to form covalent bonds. Silanes are therefore ineffective at priming many substrates, especially metal substrates on which hydroxyl groups are not available for bonding. Yet another drawback of silanes and titanates is that they tend to be hazardous materials, posing health and safety hazards and increasing costs associated with their use.
Sensitizing agents, such as stannous chloride, may be used on certain substrates, for example, glass, to roughen the surface to improve adhesion. However, any physical modification to the substrate is considered undesirable in almost all microlithography applications.
It would therefore be a significant advancement in the art to provide an improved priming composition that is non-hazardous and functions both as an effective cleaner and adhesion promoter so as to eliminate the need for separate wet process cleaning and priming of substrates prior to photoresist application, yet is sufficiently versatile to permit it to be used for priming metallic or non-metallic substrates to be adhered to positive photoresist or negative photoresist.
It is, therefore, an object of this invention to achieve the above-discussed advancement in the art by the provision of an improved primer composition that is non-hazardous, yet sufficiently versatile to bond metallic and non-metallic substrates to a positive or negative photoresist.
In accordance with the principles of this invention, these and other objects are achieved by the provision of a priming composition which may be coated on a substrate and is capable of creating covalent bonds with both the substrate and a subsequently applied photoresist to thereby link the substrate to the photoresist.
In accordance with an embodiment of this invention, the priming composition comprises at least one water-soluble polymer having a plurality of substituents derived from cyclic ethers. The backbone of the polymer may be formed, by way of example and without limitation, from tertiary amines or quaternary ammonium compounds. The backbone may be derived from one or more compounds containing cyclic nitrogen-containing rings, such as aziridines and imidazoles. In cases in which one of these representative backbones is selected, the cyclic ethers are grafted onto nitrogen atoms of the backbone. The cyclic ether is preferably an epoxide, such as ethylene oxide and/or epichlorohydrin. Representative polymers include hydroxyethylated polyethylene imine and polyethylene imine epichlorohydrin.
Because the polyelectrolyte is water soluble, it allows for greater versatility with respect to ingredients that may be included in the priming composition. The priming composition optionally may include one or more of the following, in any combination: at least one alcohol capable of increasing the stability and wetting properties of the priming composition; at least one member selected from the group consisting of alcohol ethers and ether acetates; at least one non-ionic surfactant; and/or at least one detergency enhancing agent. The pH of the priming composition may be modified to provide optimum performance through the addition of an organic acid. For example, for polyethylene iminexe2x80x94epichlorohydrin, the pH is preferably between about 3.5 and about 7.
Some materials may be incompatible with certain embodiments of this invention and generally should be avoided. These materials include the following: mercaptans; strong oxidizing or reducing agents (although such agents may be added in diluted form); dextran sulfates and other sulfates or phosphate compounds that may be bound to any free amines. With regard to phosphate and sulfate compounds, these compounds may provide some benefit when added in a polyprotic acid form so as to act as counter ions to the polyelectrolyte. Other incompatible materials include ionic constituents, such as anionic wetting agents which may reactive with the ether rings and interfere with the charge density site on which the cyclic ether is grafted.
Another object of the invention is to provide microelectronic components having improved physical and performance properties comprising a photoresist bonded to a substrate with the inventive priming composition.
In accordance with the principles of this invention, these and other objects are attained by the provision of microelectronic components comprising: a substrate, such as silicon, glass, indium tin oxide, gallium arsenate, nickel, and the like; an effective amount of a film of the priming composition of the invention carried on and bonded to at least one surface of the substrate; and a layer of a negative or positive photoresist bonded to the substrate by the priming composition described above.
A further object is to provide an economical method of applying the embodiments of the inventive priming composition to a substrate prior to coating with a photoresist in a more flexible and efficient manner than presently known.
In accordance with the principles of this invention, these and other objects are attained by the provision of a method of cleaning or cleansing at least one surface of a substrate and bonding of a photoresist layer subsequently applied to the cleaned surface. This method generally comprises: washing at least one surface of a substrate (e.g., silicon, glass, indium tin oxide, nickel, and gallium arsenate) with an effective amount of the priming composition of the invention sufficient to bind the polyelectrolyte to the substrate via covalent bonds formed by first oxygen atoms of the cyclic ethers; optionally rinsing the washed surface with an aqueous solution sufficient to remove contaminants and leave a thin film of priming composition on the cleaned surface; applying a layer of photoresist to the cleaned surface; and curing the layer of photoresist under conditions which cause the film of priming composition to form covalent bonds with the photoresist via second (residual) oxygen atoms of the cyclic ethers and thereby link the substrate to the photoresist.
Still a further object is to provide an economical method of applying the inventive priming composition to the substrate at the same time the photoresist is applied to the substrate to provide an even more flexible and efficient manner than presently known.
In accordance with the principles of this invention, these and other objects are achieved by premixing the inventive priming composition with a photoresist precursor composition to form a pre-primed photoresist composition. In this variant embodiment, the priming composition by pre-dissolved in a solvent compatible with the photoresist. This variation allows for the elimination of separate priming and photoresist coating steps.
These and other objects, features, and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying figure which illustrates, by way of example, the principles of the present invention.